I've been teaching light as wave (and then light as a particle) for years, but only last year did the words "We don't actually see light" (as a wave) come out of my mouth. I then paused and said "but of course seeing light is actually what seeing is". The class and I looked at each other like we were all deer caught in the headlights. I think we were all on the same page at that moment in the classroom, but it is a bit linguistically problematic, isn't it?
Every year, at least one student will ask a question that reveals that age-old misconception that comes from our describing light as a transverse wave: they are trying to picture photons going in a wave-like path on their way from source to sink. Adding to, not helping this easy-to-make mistake is the classic picture of light as an propagating electric & magnetic field:
Look - there's stuff going up & down (& sideways!). This is what we show the students to justify calling it a transverse wave. But, nothing is actually "going" up or down. Those arrows represent field intensities getting bigger and smaller (and changing direction) along the central arrow. This picture assume a relatively sophisticated understanding of vector fields which first year physics student don't have.
A picture is worth a thousand words, but what if 500 hundred of those words are the wrong words?
Saturday, September 21, 2013
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Valid point Rideout. Much of the time teachers assume students understand things prior to class lectures; this is a clear misconception. (E.g.) I wonder if Kamal knows what a vector is on this very day. -Matt Goddard
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